diff --git a/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/EntityModeConverter.java b/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/EntityModeConverter.java
index eeee468ba2..d9548064fa 100644
--- a/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/EntityModeConverter.java
+++ b/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/EntityModeConverter.java
@@ -17,6 +17,6 @@ public class EntityModeConverter {
 	}
 
 	public static String toXml(EntityMode entityMode) {
-		return entityMode.name();
+		return ( null == entityMode ) ? null : entityMode.getExternalName();
 	}
 }
diff --git a/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/GenerationTimingConverter.java b/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/GenerationTimingConverter.java
index 55b7d93053..546bc0801c 100644
--- a/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/GenerationTimingConverter.java
+++ b/hibernate-core/src/main/java/org/hibernate/boot/jaxb/hbm/internal/GenerationTimingConverter.java
@@ -19,6 +19,8 @@ public class GenerationTimingConverter {
 	}
 
 	public static String toXml(GenerationTiming generationTiming) {
-		return generationTiming.name().toLowerCase( Locale.ENGLISH );
+		return ( null == generationTiming ) ?
+				null :
+				generationTiming.name().toLowerCase( Locale.ENGLISH );
 	}
 }
diff --git a/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/EntityModeConverterTest.java b/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/EntityModeConverterTest.java
new file mode 100644
index 0000000000..7bf232d7c5
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/EntityModeConverterTest.java
@@ -0,0 +1,49 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.test.boot.jaxb.hbm.internal;
+
+import org.hibernate.EntityMode;
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmHibernateMapping;
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmRootEntityType;
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmSimpleIdType;
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmTuplizerType;
+import org.hibernate.tuple.entity.DynamicMapEntityTuplizer;
+
+import org.hibernate.testing.junit4.BaseUnitTestCase;
+import org.junit.Test;
+
+/**
+ * @author Jean-François Boeuf
+ */
+public class EntityModeConverterTest extends BaseUnitTestCase {
+
+	@Test
+	public void testMashallNullEntityMode() throws Exception {
+		XmlBindingChecker.checkValidGeneration( generateXml( false ) );
+	}
+
+	@Test
+	public void testMashallNotNullEntityMode() throws Exception {
+		XmlBindingChecker.checkValidGeneration( generateXml( true ) );
+	}
+
+	private JaxbHbmHibernateMapping generateXml(boolean includeEntityMode)
+			throws Exception {
+		JaxbHbmHibernateMapping hm = new JaxbHbmHibernateMapping();
+		JaxbHbmRootEntityType clazz = new JaxbHbmRootEntityType();
+		JaxbHbmTuplizerType tuplizer = new JaxbHbmTuplizerType();
+		tuplizer.setClazz( DynamicMapEntityTuplizer.class.getCanonicalName() );
+		if ( includeEntityMode ) {
+			tuplizer.setEntityMode( EntityMode.MAP );
+		}
+		clazz.getTuplizer().add( tuplizer );
+		JaxbHbmSimpleIdType id = new JaxbHbmSimpleIdType();
+		clazz.setId( id );
+		hm.getClazz().add( clazz );
+		return hm;
+	}
+}
diff --git a/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/GenerationTimingConverterTest.java b/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/GenerationTimingConverterTest.java
new file mode 100644
index 0000000000..98d29cbc30
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/GenerationTimingConverterTest.java
@@ -0,0 +1,37 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.test.boot.jaxb.hbm.internal;
+
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmBasicAttributeType;
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmHibernateMapping;
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmRootEntityType;
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmSimpleIdType;
+
+import org.hibernate.testing.junit4.BaseUnitTestCase;
+import org.junit.Test;
+
+/**
+ * @author Jean-François Boeuf
+ */
+public class GenerationTimingConverterTest extends BaseUnitTestCase {
+
+	@Test
+	public void testMashallAttributeWithNullGenerationTiming()
+			throws Exception {
+		JaxbHbmHibernateMapping hm = new JaxbHbmHibernateMapping();
+		JaxbHbmRootEntityType clazz = new JaxbHbmRootEntityType();
+		JaxbHbmSimpleIdType id = new JaxbHbmSimpleIdType();
+		JaxbHbmBasicAttributeType att = new JaxbHbmBasicAttributeType();
+		att.setName( "attributeName" );
+		clazz.getAttributes().add( att );
+		clazz.setId( id );
+		hm.getClazz().add( clazz );
+
+		XmlBindingChecker.checkValidGeneration( hm );
+	}
+
+}
diff --git a/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/XmlBindingChecker.java b/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/XmlBindingChecker.java
new file mode 100644
index 0000000000..21d9c30aac
--- /dev/null
+++ b/hibernate-core/src/test/java/org/hibernate/test/boot/jaxb/hbm/internal/XmlBindingChecker.java
@@ -0,0 +1,38 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.test.boot.jaxb.hbm.internal;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+
+import javax.xml.bind.JAXBContext;
+import javax.xml.bind.Marshaller;
+
+import org.hibernate.boot.jaxb.hbm.spi.JaxbHbmHibernateMapping;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.hibernate.boot.spi.XmlMappingBinderAccess;
+import org.hibernate.service.ServiceRegistry;
+
+/**
+ * @author Jean-François Boeuf
+ */
+public class XmlBindingChecker {
+
+	public static void checkValidGeneration(JaxbHbmHibernateMapping hbmMapping)
+			throws Exception {
+		JAXBContext jaxbContext = JAXBContext
+				.newInstance( JaxbHbmHibernateMapping.class );
+
+		Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
+		jaxbMarshaller.setProperty( Marshaller.JAXB_FORMATTED_OUTPUT, true );
+		ByteArrayOutputStream bos = new ByteArrayOutputStream();
+		jaxbMarshaller.marshal( hbmMapping, bos );
+		ByteArrayInputStream is = new ByteArrayInputStream( bos.toByteArray() );
+		ServiceRegistry sr = new StandardServiceRegistryBuilder().build();
+		new XmlMappingBinderAccess( sr ).bind( is );
+	}
+}